The present invention relates to large-vehicle refrigeration systems (reefers) and more particularly to semi-truck reefers.
The prior art systems employ internal combustion engines to directly drive the compressor and other components of the reefer. Modern electrical reefer systems use an internal combustion engine to run a generator that produces alternating current (ac) power to drive an ac motor and other ac components.
While the apparatii of the prior art fulfills their particular objectives they do not eliminate carbon exhaust emissions. Some of these designs simply store electric energy to be used at some later time. Others use a combination of an ac electric motor and a diesel engine that emits carbon exhaust emissions. Therefore they do not meet idle restriction limits or emissions standards. These units are based on ac power and are not readily adaptable to battery power and emissions free operation.
It completely eliminates particulate and carbon exhaust emissions from these reefers especially during the critical phases of food transport, loading and unloading. This invention uses a battery powered direct-current (dc) electric motor instead of an internal combustion engine, thus providing for the first time a self-contained, all electric semi-trailer reefer system that is economical to operate and simple to manufacture. It also meets the rigorous demands of the trucking industry and environmental idle and emissions mandates.
In order to use a battery to power one of these ac systems the dc battery power must be continually inverted to single phase ac power thus wasting critical battery power and introducing reliability issues. This single phase power does not work well because the inrush current is too high with a single phase ac motor. So the ac power from the inverter must be converted to 3 phase using a variable frequency drive to run a 3 phase ac electric motor. This wastes battery power and adds expense. Also the generator power of an ac system must be inverted to dc power to charge a battery. These multiple power inversions are expensive, require additional maintenance, waste battery power and are not economically feasible. This has been a limiting factor in designing a production worthy all electric system prior to this invention.
Generator/alternator systems that are AC based, must use constant generator-rotational speed configurations to match the 60 cycle frequency requirements of an ac motor. This is done mechanically with transmissions and hydraulically with constant speed pumps. These configurations are expensive, maintenance heavy and unreliable making them ill suited to reefer applications.
The reefer dc electric motor of this invention is driven by simple dc power from the battery and generator combination and is not prone to the issue of variable generator rpm and the associated frequency fluctuations of an ac generator output. These issues and power loses are eliminated by the all dc power design of this invention.
An object of the invention is to provide a high-performance power system that routinely generates and uses dc-only power at or in excess of 18 Kw. Reliability issues occur with the constant on and off switching of the high power that drives the heavy duty electric motor. Electrical spiking and thermal over-temperature conditions occur frequently, which require special circuit designs and protection.
This is especially true of the ac electric and diesel system since it must constantly switch between electric and diesel power. Existing power management techniques have failed to take this into account which is another major reason why an all electric semi-trailer reefer system has not been successfully designed to date.
The simple dc power control system of this invention avoids these reliability issues. Some of the prior art apparatii use a separate axle to drive the generator such as a third axle. Typically this axle must have a control system that lifts the wheels off the road surface when the generator is not being used, or when a tight turn is made, or when backing up. These axles are very undesirable because they modify the trailer suspension system. Safety rules are violated and road worthiness is degraded. Separate axle configurations produce abnormal tire wear from side load scuffing and abrupt wheel rotation when lowered to the road surface.
This invention eliminates these issues by driving the generator with an axle and differential mounted to the standard trailer suspension.
The prior art devices lack the features necessary to physically replace the reefer internal combustion engine, which is usually diesel.
This invention makes possible for the first time the fabrication or retrofit of a semi-trailer reefer system that is all electric and completely self contained. Self contained in the sense that this reefer trailer system has within itself all the components needed to refrigerate during all phases of food transport and delivery independent of the tractor.
A unique combination of high-power generator, compressor, heavy-duty axle/differential, batteries and direct current power control and motor system achieve the cooling capacity necessary and sufficient for the refrigeration trucking industry.
If more refrigeration capacity is needed during the battery power-only phase of operation cold air containment curtains and/or eutectic plates are added to the all electric reefer system. Air containment curtains are track operated at the semi-trailer delivery door to allow easy ingress and egress while reducing the escape of refrigerated air to the outside atmosphere. Eutectic plates store cooling capacity generated during road or line power reefer operation in a eutectic solution contained by plates that can be part of the reefer evaporator section.
A small portable auxiliary battery may be used to provide emergency power. This extra cooling capacity is then available during the critical power limited phase of operation when the all electric reefer system is stationary and no additional power is supplied to the battery.
The generator cannot be mounted in the semi-tractor engine compartment. One-piece trucks can use a smaller generator mounted to the truck engine to run the smaller reefer unit and charge the batteries. This does not work for a semi-tractor/trailer combination because the logistics of mixing and matching tractors with trailers are too restrictive during normal operations. Therefore a semi-trailer specific generator is required. This invention makes use of the semi-trailer motion to drive an electric generator.
It is a matter of converting the translational vehicle momentum to rotational momentum. The electric generator is programmed to not produce electricity during any acceleration phase thus, it never puts a load on the semi-tractor engine during acceleration of the vehicle. A semi-trailer is but one example. Generally this power generation system can be applied to any vehicle in motion where there is the capacity to have rotation.
Heavy duty construction of the axle and generator is compatible with and takes advantage of the large mass of the semi-tractor/trailer to make electric power. This power from the generator charges batteries and runs the electric refrigeration unit and its electric motor whenever the vehicle is in motion. The combination of battery power and dc electric motor replaces the internal combustion engine typically used to power reefers thus eliminating their exhaust emissions.
In some cases a compressor with a built-in electric motor is used. Stored battery power runs the refrigeration unit electric motor when the vehicle is stationary and remote. Line power is used to charge the batteries and run the electric refrigeration unit during situations where the vehicle is stationary and line power is available.
This all electric reefer system meets idle restriction mandates and emission standards. All components of the power and refrigeration systems can be mounted to a semi-trailer making it self contained and independent of the tractor configuration. The axle and differential are mounted to the normal suspension of the semi-trailer thus assuring this all electric semi-trailer reefer system will meet existing road worthiness laws. This mobile power system can be mounted on a variety of vehicles and used to run many different types of electrical units.